1. Field of the Invention
The present invention relates to a laminating method and a laminating apparatus for manufacturing a photovoltaic module.
2. Description of Related Art
As a laminating apparatus for manufacturing a photovoltaic module, there has been a one disclosed in Japanese Patent Application Laid-open Publication No. 9-141743 or a one disclosed in Japanese Utility Model Publication No. 3037201. A conventional laminating apparatus is generally configured by a lid having an upper chamber formed with a diaphragm expandable downwardly and a vacuum vessel main body corresponding to the lid having a lower chamber equipped with a heating plate. In a state that the lid is opened, there is mounted a multilayer material to be processed on the heating plate provided in the lower chamber of the main body. The multilayer material is configured by a sequential stacking of a glass plate as a lowermost layer, a sheet-like filler, photovoltaic modules and another sheet-like filler, with a sheet-like backing member mounted as an uppermost layer. Then, the upper chamber and the lower chamber are pressure-reduced and the multilayer material is heated. The air or the atmosphere is introduced into the upper chamber so that the multilayer material is sandwiched between an upper surface of the heating plate and the diaphragm to be laminated with pressure.
In the above, the pressure-reduction, namely evacuation, is conducted in the upper chamber and the lower chamber in order to prevent air void from remaining in the multilayer material. The reduction is because, when the photovoltaic module including the remaining air void is exposed to sunlight and its temperature rises, the air void are expanded to accelerate degradation of the photovoltaic module.
Also, the multilayer material is heated by the heating plate while the temperature of the heating plate is being controlled to a set temperature. After a lapse of an appropriate time period, the temperature of the multilayer material becomes approximately equal to the temperature of the heating plate. Therefore, when the set temperature is a temperature above the melting point of the filler, the filler melts, and the air is introduced into only the upper chamber so that the diaphragm is inflated to press the multilayer material against the heating plate to laminate the multilayer material with the heating plate into one unit. After this laminating, the lower chamber is restored to the atmospheric pressure, and the lid is opened to take out the multilayer material.
On the other hand, EVA (ethylene-vinyl-acetate) resin is used as a filler. When the EVA resin is used, it melts at about 80xc2x0 C. to 110xc2x0 C. Therefore, in the laminating apparatus, the resin is melted at the above temperature range or above and it is laminated by pressing.
However, according to the above-described conventional laminating apparatus, in manufacturing a photovoltaic module of a relatively large size of 1 square meters, for example, the temperature of the lower surface of the multilayer material in contact with the heating plate rises easily but the temperature of the upper surface does not rise so easily as that of the lower surface. Therefore, there arises a difference in temperatures between the upper surface and the lower surface. Because of this temperature difference, such a phenomenon arises that both ends of a multilayer material A are warped upwards as compared with the center portion, as shown in FIG. 9. Once this warp occurs, the end portion of the warp is separated from the heating plate 11, so that the temperature does not rise easily. Accordingly, it takes a long time to raise the temperature of the multilayer material A as a whole to a uniform temperature, resulting in poor productivity.
When the air is introduced into the upper chamber and the multilayer material is pressed with the diaphragm, the warped multilayer material A is pressed against the heating plate 11 and the temperature of the end portion is made to rise easily. However, with this arrangement, the multilayer material is pressed before the EVA is sufficiently melted, which has a risk of a frequent occurrence of a phenomenon that the photovoltaic modules are broken. In FIG. 9, a reference numeral 7 denotes a vacuum vessel main body, a reference numeral 12 denotes a lower chamber, and a reference numeral 13 denotes a sealing member for sealing a lid (not shown) provided on the vessel main body 7 from the above.
On the other hand, when the photovoltaic modules are made much larger, it becomes necessary to make larger the thickness of the glass plate of the lowermost layer for securing the strength. However, when the glass plate has a large thickness, the temperature difference between the upper surface and the lower surface of the multilayer material becomes much larger, and this has a risk of a breaking of the glass plate.
In view of the above conventional technique, an object of the present invention is to provide a laminating method and a laminating apparatus for manufacturing large-type photovoltaic modules in satisfactory productivity with minimum occurrence of warp of a multilayer material, by making smaller the temperature difference between an upper surface and a lower surface of the multilayer material.
A laminating method in the manufacture of photovoltaic modules according to the invention which aims at solving the above problems is characterized in that, in a manufacture of photovoltaic modules configured by a surfacing member, a filler, photovoltaic modules, another filler and a backing member, the surfacing member and the backing member are heated from the outside to melt the fillers. Further, a laminating apparatus for implementing this method is a laminating apparatus having an upper chamber and a lower chamber partitioned by a diaphragm, wherein a heating plate incorporating a heater is disposed within the lower chamber and one or a plurality of flexible heaters are disposed between the lower chamber and the diaphragm.
In other words, according to the laminating method of the invention, a multilayer material configured by a surfacing member, a filler, photovoltaic modules, another filler and a backing member is heated from both the front surface and the back surface to melt the fillers so that these members are laminated. This avoids an occurrence of warp and provides a satisfactory heat conduction. Productivity is improved by this arrangement. When a glass plate is used as a surfacing member, its internal stress can be decreased to prevent an occurrence of cracking.
Further, according to the laminating method of the invention, in the case of laminating by a laminating apparatus having an upper chamber and a lower chamber partitioned by a diaphragm, a multilayer material to be processed is set within the lower chamber, followed by an evacuation of the lower chamber, and a gas is introduced into the upper chamber for pressing. At first, the pressing is conducted at a low pressure, and thereafter, the pressing is conducted at a high pressure. This causes the photovoltaic modules to be pressed against the heating plate without generating a crack in the photovoltaic modules, and also promotes a uniform distribution of the temperature of the multilayer material. After the temperature is raised uniformly, the pressing is conducted at a high pressure, and thus the lamination is completed.
A laminating apparatus for implementing the above laminating method has a heating plate incorporating a heater within the lower chamber, and also has at least one flexible heater between the lower chamber and the diaphragm. This is because it is preferable that the heaters are deformed along the multilayer material when the multilayer material is pressed.
Further, in the case of providing flexible heaters, it is possible to obtain a satisfactory uniform distribution of temperatures within the range of pressing when a large number of flexible heaters are divided into a plurality of groups and temperature is controlled for each group. Further, when the plurality of flexible heaters are provided such that each individual heater can be taken out, it becomes possible to replace only a heater which has a problem of a dislaminateion or the like. This can minimize a loss.
In the above-described laminating apparatus, there may be disposed a sheet-like heating unit between the lower chamber and the diaphragm. This sheet-like heating unit is provided by sandwiching a conductor with rubber sheets to form a heater, then laminateing this heater with a flexibly bendable and not-easily stretchable sheet, and by laminateing this sheet with a stretchable elastic sheet. By laminateing the heater with the flexibly bendable and not-easily stretchable sheet, this sheet prevents the heater from being stretched when the heater is deformed along the multilayer material by a pressing. Thus, the life of the heater is made longer until it is dislaminated. However, when the length of this sheet-like heating unit is in short although it can lie along the multilayer material, the heating unit cannot keep a close adhesion to the multilayer material. This can be solved when a stretchable elastic sheet is laminated to both ends of the sheet. A flexibly bendable and not-easily stretchable sheet includes a rubber sheet having a glass fiber as a core material. A stretchable and elastic sheet includes a silicone rubber sheet, or the like.
Then, in the heating plate incorporating a heater within the lower chamber and the at least one flexible heater disposed between the lower chamber and the diaphragm, a temperature control is carried out by not conducting a current to the other when a current is conducted to the one. With this arrangement, a maximum current conducted does not become large despite a fact that a heating is applied from both the lower and upper surfaces. Thus, a large power supply facility is not necessary.
As another laminating apparatus for implementing the laminating method of the invention, there may be provided such a configuration that a heating plate incorporating a heater is provided within a lower chamber and a heater is provided within an upper chamber. It is possible to conduct heat to the diaphragm by a radiant heating from the heater inside the upper chamber and a heat conduction of the gas, thereby to heat a multilayer material through the diaphragm.
Further, as another laminating apparatus for implementing the laminating method of the invention, there may be provided such a configuration that a heating plate incorporating a heater is provided within a lower chamber and a heater for heating the gas and a blower for circulating the heated gas are provided within an upper chamber. With this arrangement, the gas heated within the upper chamber is circulated forcibly to conduct heat to a diaphragm for heating a multilayer material.
As a laminating apparatus for implementing the laminating method by using a laminating apparatus having the upper chamber and the lower chamber partitioned by the diaphragm, with the lower chamber evacuated and a gas introduced into the upper chamber, for pressing at a low pressure at the beginning and thereafter pressing at a high pressure to carry out a lamination, there may be provided a plurality of pressure setters so as to be able to change the pressure within the upper chamber. According to this laminating apparatus, it is possible to operate as follows, as an example. A low pressure is set to one pressure setter and a high pressure is set to the other pressure setter. In the case of pressing at a low pressure, the gas is introduced into the upper chamber until when the pressure setter set with the low pressure operates. At a point of time when the pressure setter set with the low pressure operates, the introduction of the gas is stopped and the pressure is maintained. Thereafter, for pressing at a high pressure, the gas is introduced into the upper chamber again. At a point of time when the setter set with the high pressure operates, the introduction of the gas is stopped and the pressure can be maintained. When the introduction of the gas is stopped and the pressure is maintained for a relatively long time, the gas inside the upper chamber inflates by the heat and the inside pressure increases. In this case, at a point of time when it is detected that the inside pressure is higher than the set pressure, the vacuum valve is opened momentarily to return the pressure to the set pressure, thereby to maintain the pressure at a constant level, for example.
As a laminating apparatus for implementing the laminating method by using a laminating apparatus having the upper chamber and the lower chamber partitioned by the diaphragm, with the lower chamber evacuated and a gas introduced into the upper chamber, for pressing at a low pressure at the beginning and thereafter pressing at a high pressure to carry out a lamination, there may be provided a plurality of timers for setting a time for introducing the gas into the upper chamber. In other words, when this laminating apparatus is used, the gas is introduced to carry out a pressing at a low pressure until when one timer starts operating. After maintaining the pressure for a suitable period of time, the gas is introduced again. The introduction of the gas is stopped at a point of time when the other timer starts operating, so that a high-pressure pressing can be carried out.